Exclude pinned vertices from physics simulation
Unfortunately this is not possible as I showed here as well. However, this should be possible if you are willing to dig into Blender's source code and figure out how to ignore the calculations done on pinned vertices. If you are willing to do that, you need to look into the code in softbody.c and see where you can make the necessary changes and then recompile Blender to get the desired behavior.

As I explained here Blender's soft body physics solver will go under significant overhaul in the future and doing what you want looks to be definite possibility once the new system has been put in place. This will take a couple of months though.